In replacing a knee joint which has been damaged due to disease or trauma, it is important that the prosthesis used to replace the damaged portion of the joint be properly aligned with respect to the bone to which the prosthesis is fixed. If the tibial surface does not lie in the correct plane, the implanted prosthesis may not properly articulate with the distal femoral prosthesis when the knee joint is reduced, and complications can result. Particular problems are encountered when resection of either the medial or lateral tibial surface is required, in that available shaping instruments require sacrificing the entire proximal surface. Rather, the stability of the prosthesis and knee is significantly improved by retaining as much of the proximal surface as possible.